1. Field of the Invention
This invention relates to the field of multiple source high-power sound systems, and in particular, to high fidelity, high intelligibility sound transmission systems for concerts and the like.
2. Prior Art
Audio speaker systems of particularly high power are commonly used for concerts delivered in auditoriums, arenas and amphitheaters, both indoors and outdoors. Typically, individual speakers or "boxes" are stacked or "flown" in a large, closely spaced array in multiples. A typical "wall of sound" system as known in the prior art is shown in FIG. 1, and generally designated by reference numeral 10. A large array of speakers is often referred to as a "concert rig". The concert rig 10 comprises four speaker systems, designated 12, 14, 16 and 18, disposed on a straight line 20. Each speaker system comprises loudspeakers of different sizes and designs, which are appropriate for efficiencies in bass response, mid frequency response and high frequency response, respectively. The four speaker systems interact with one another, creating a plurality of different zones across the listening area or composite zone, wherein sound emitted by each of the speaker systems will remain pure and undistorted, or will be mixed with sounds emitted from one, two or three of the other speaker systems, creating sound confusion and loss of intelligibility. The principal cause of intelligibility loss in the arrival of sound from various sources at different times. Due to path length differences. The different zones are marked and shaded according to the chart shown in FIG. 4. The zones of purest sound are clear, without shading, and identified by the numeral 1. The least intelligible, most distorted sound is shaded the darkest, and identified by numeral 5. Pure sound, that is, sound which is emitted from only one source, and is not mixed with sound emitted from any other source, is transmitted along the outer edges of the zone and immediately in front of each of the speaker systems, as indicated by numeral 1. A number of short zones 2, known as "hi-fi alleys" are formed. The sound in each of the hi-fi alleys emanates from two sources, but inasmuch as the sound contribution from each of the two sources is substantially equal, the overall sound is of generally good quality. Zones designated by reference numeral 3 indicate sound confusion and loss of intelligibility due to unequal contribution from two sources. Zones marked by reference numeral 4 denote more confusion and loss of intelligibility, due to unequal contributions from three sources. The zone designated by reference numeral 5, which will be the single largest zone in the listening area, indicates maximum confusion and interference and maximum loss of intelligibility, due to unequal sound contributions from all four sources. It will be appreciated by those skilled in the art, and indeed by those who attend concerts where such concert rigs are utilized, that more than four speaker systems or sources are often used, for example six to eight sources for covering a wide angle zone of 100 degrees or more. Four sources are illustrated in FIG. 1 in order to reduce the difficulty of illustrating the problems of the prior art without unduly complicating the drawing.
A further difficulty stems from a demand perceived by the those presenting concerts to provide the maximum in sound level, which in turn requires the generation of high sound pressure levels and high dynamic range. Many concert boxes are literally filled with amplifiers and related devices in order to generate as much sound power as possible. Concert rigs such as that shown in FIG. 1 have, unfortunately for those presenting and attending concerts, become synonymous with load sound of inferior quality.
Some improvement has been achieved by a concert rig 30 as shown in FIG. 2, wherein each of the speaker systems or sources 32, 34, 36 and 38 are splayed outwardly from one another, being disposed upon a common arc or shallow curve 40. This arrangement has the effect of modestly increasing the size of the zones 1 of pure sound and the zones of hi-fi alleys 2 of equally mixed sounds. However, it is easily seen that the vast majority of the composite listening zone comprises sound zones designated 3, 4 and 5, which are of noticeably inferior quality. The angle between such splayed sources is typically between ten degrees and twenty degrees, and the system is intended to cover an overall zone of between sixty degrees and ninety degrees. The multiple overlap of sound generated by each of the typical concert rigs 10 and 30 shown in FIGS. 1 and 2 results in a highly unintelligible, acoustically blurred sound quality. Only those listeners who are very close to any one of the individual systems will receive relatively intelligible and undistorted sound. Such listeners are also likely to be deafened by the sound pressure levels.
This invention overcomes the difficulties of the prior art by providing a composite listening zone in which pure, unmixed, undistorted sound is delivered to virtually 100 percent of the listening zone, by emitting sound waves from a plurality of individual electroacoustical sources, each of a constant directivity type and characterized by a relatively narrow, wedge-shaped envelope of sound projection, such that adjacent edges of respective sound projection envelopes are in substantial alignement and do not overlap. The absence of interference between sounds emitted from different ones of the sources precludes sound distortion and enables uniform sound dispersion and high sound quality through the listening zone. Even the extent to which sound from adjacent sources may mix, it mixes equally in hi-fi alleys, a situation which provides at least good sound quality, if not the best sound quality. This can be appreciated by reference to the concert rig 50 shown in FIG. 3, which will be described in detail hereinafter.